Precast concrete formwork, floor system and a method of construction

ABSTRACT

Formwork for constructing a floor system in a building, the formwork comprising: a plurality of pre-cast concrete joists positioned in a generally parallel arrangement, wherein one or more of the joists comprises: a horizontal base portion; and an upwardly directed portion extending substantially along the length of the joist, the upwardly directed portion having spaced apart surfaces extending upwardly from the base wherein respective shelf portions of the base are located adjacent said upwardly directed portion; a plurality of pre-cast concrete members for extending along a length of the joists for receiving wet concrete; and a supporting arrangement to support opposite ends each of the pre-cast concrete members upon oppositely arranged shelf portions of two adjacent joists.

TECHNICAL FIELD

The present invention relates to the field of construction and more specifically relates to a floor system and an associated method of forming a floor system.

BACKGROUND

Any references to methods, apparatus or documents of the prior art are not to be taken as constituting any evidence or admission that they formed, or form part of the common general knowledge.

Suspended flooring systems with pre-cast components are gaining popularity for both residential and commercial construction projects. Formwork is a structural component that is temporarily used during construction phase and plays a significant role in the concrete building industry. Improper design of the formwork may cause partial or full collapse of a building during construction and/or excessive cracking and deformation at the operational stage. Furthermore, inappropriate stiffness of the formwork affects the surface finishes of the concrete structure. Therefore, a stiff formwork results in a flatter and smoother finish.

The shape of the formwork is also affected by the shape of the final structural elements. Hence, preparation and assembling of formworks can be time consuming and a costly process. Eliminating the step of preparation and assembling of formwork is also highly desirable because minimizing the use of formwork may enhance safety for construction personnel and increase the speed of construction whilst also decrease the cost associated with it.

Depending on the slab type, steel or timber formworks have been previously used. In some instances, where propping of the formworks is not possible precast concrete slabs have been used.

One of the commonly used floor systems with precast concrete slabs comprises joists and blocks. The joists are mostly placed with gaps ranging between 400 to 600 mm. The gap between the joists is filled with concrete or other types of masonry blocks and the joists and blocks are subsequently covered by a fresh concrete overlay of 60 to 120 mm thick concrete layer. The system acts as a one-way ribbed slab. Such a floor system uses a simple construction method but can be time consuming and is not suitable for use in long spans and normally results in a thick floor system.

Another commonly used floor system is known as the composite floor system. Composite floors are mostly used with steel structures. The distance between beams used in these systems varies from 900 mm to 3000 mm with economical distance of about 1200 mm to 2400 mm. Steel beams used in these system must be fire rated to meet relevant building code requirements which makes these floor systems expensive. Further, shear studs must be installed at the top flange of the beam to shape proper connections between the concrete slab and the supporting steel beam. The process of installing such composite floor systems can be time consuming and demands onsite welding and the integrity of the system depends on the strength of shear studs and their connections to the steel beam.

Yet another floor system is known as the waffle slab system. The waffle slab system comprises a two-way slab that is made of GRP (fibreglass) moulds. The system contains integrated joists that extend in both directions. The distance between joists varies between 600 mm to 1200 mm. Even though, the waffle slab system is suitable for covering long spans, this system is not economical for use in large scale construction. Construction of the waffle type slab system can also be time consuming.

There is a need for providing an improved floor system that overcomes the deficiencies of the prior art floor systems.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides formwork for constructing a floor system in a building, the formwork comprising:

-   -   a plurality of pre-cast concrete joists positioned in a         generally parallel arrangement, wherein one or more of the         joists comprises: a horizontal base portion; and an upwardly         directed portion extending substantially along the length of the         joist, the upwardly directed portion having spaced apart         surfaces extending upwardly from the base wherein respective         shelf portions of the base are located adjacent said upwardly         directed portion;     -   a plurality of pre-cast concrete members for extending along a         length of the joists for receiving wet concrete; and     -   a supporting arrangement to support opposite ends each of the         pre-cast concrete members upon oppositely arranged shelf         portions of two adjacent joists.

In one embodiment, one or more of the pre-cast concrete members comprises a shell for receiving wet concrete, the shell being adapted to be coupled with respective downwardly directed supporting portions for supporting the shell on the oppositely arranged shelf portions of two adjacent joists.

In an embodiment, the supporting portions are integrally formed with the pre-cast members.

In an alternative embodiment, each of the pre-cast supporting portions comprises an in-use lower portion for being positioned on the respective shelf portions and an in-use upper portion for being coupled with lateral ends of the pre-cast members.

In an embodiment, the supporting portions are adapted to extend along a length of the joist.

In an embodiment, an outer surface of the pre-cast concrete members in combination with the surface of the upwardly directed portion of the supporting joists positioned at opposite ends defines an in-use receiving portion for receiving wet concrete.

In an embodiment, the pre-cast concrete members comprises edge portions extending along a length of the pre-cast concrete members wherein preferably at least a first edge portion extends along a first lateral side of the pre-cast concrete member and at least a second edge portion extends a second lateral side of the pre-cast concrete member.

In an embodiment, one or more of the pre-cast concrete members comprises:

-   -   a pan for receiving the wet concrete; and     -   shoulder portions located at opposite ends of the pan, said         shoulder portions being adapted to be supported on the         oppositely arranged shelf portions of two adjacent joists.

In an embodiment, the pan in combination with the surface of the upwardly directed portion of the supporting joists positioned at opposite ends defines an in-use receiving portion for receiving wet concrete.

In an embodiment, the pre-cast concrete joists are supported by a plurality of beams extending generally in a perpendicular direction relative to the general direction of the said pre-cast concrete joists.

In an embodiment, the beam comprises a beam portion with a substantially flat profile with two spaced apart formations extending upwardly from the beam portion, the said formations extending along a length of the beam and joist receiving portions extending outwardly from the said formations for supporting an end portion of a plurality of joists.

In an embodiment, an outwardly projecting end portion of the plurality of joists is supported upon a joist receiving portion of the beam portion, the joist receiving portion of the beam preferably extending in a perpendicular direction relative to the said projecting end portions of the joist.

In an embodiment, an underside bottom surface of the beam substantially lies in the same plane as a bottom surface of the joist.

In an embodiment, the formwork further comprises:

-   -   a first connecting mechanism for connecting a first joist         positioned on a first lateral side of the beam with a second         joist positioned on a second lateral side of the beam, said         connecting mechanism being further adapted for preferably         applying a negative bending force to the first and second joists         during use; and     -   a second connecting mechanism for connecting two adjacently         located beams supported simultaneously on a column, the         connector being provided for applying negative bending to said         adjacently located beams.

In an embodiment, the formwork further comprises column formwork members for forming columns to support said beams wherein each of the column formwork members can be inter-connected to define a hollow portion for receiving wet concrete.

In an embodiment, end portions of each of the column formwork members comprises connecting portions for inter-connecting the column formwork members such that imaginary plane of a first column formwork member is transversely arranged relative to an imaginary plane of second column formwork member inter-connected with the first column formwork member.

In an embodiment, said locking portions extend along a longitudinal edge of the column formwork member such that in an inter-connected configuration the locking member is adapted to be received in a recess of another of said column formwork, said recess extending along a longitudinal edge of said another column formwork.

In an embodiment, the formwork further comprises one or more permanent formwork members for being positioned in between two spaced joists and wherein preferably the permanent formwork members comprise a substantially L-shaped or U-shaped cross section.

In an embodiment, the joists of the formwork further comprise one or more apertures for receiving reinforcing bars, the reinforcing bars extending in a transverse direction relative to the general direction of the joists, the reinforcing bars being adapted for being tensioned (by way of post-tensioning) after pouring concrete into the pre-cast concrete receiving members.

In another aspect, the invention provides a pre-cast concrete joist comprising: a horizontal base portion; and an upwardly directed portion extending substantially along the length of the joist, the upwardly directed portion having spaced apart surfaces extending upwardly from the base wherein shelf portions of the base are located adjacent said upwardly directed portion, each of the shelf portions defining a seat for receiving a connecting portion of a pre-cast concrete pan member or a pre-cast concrete shell member wherein height of the upwardly directed portion is equal to or greater than vertical height of the said shelf portions.

In yet another aspect, the invention provides a pre-cast concrete member for being positioned in between and supported spaced apart joists or beams, the precast member extending along a length of the joists or beams for receiving wet concrete, the precast member comprising a supporting arrangement to support opposite ends each of the pre-cast concrete members upon oppositely arranged joists or beams.

In another aspect, the invention provides a method of constructing a suspended floor in a building, the method comprising the steps of:

-   -   positioning a plurality of pre-cast concrete joists in a         generally parallel arrangement, wherein one or more of the         joists comprises: a horizontal base portion; and an upwardly         directed portion extending substantially along the length of the         joist, the upwardly directed portion having spaced apart         surfaces extending upwardly from the base wherein shelf portions         of the base are located adjacent said vertical portion;     -   positioning a plurality of pre-cast concrete members in between         adjacently located joists, said pre-cast concrete members being         positioned for extending along a length of the joists for         receiving poured concrete;     -   supporting opposite ends of each of the pre-cast concrete         members upon oppositely arranged shelf portions of two adjacent         joists; and     -   pouring fresh concrete into a receiving portion defined by the         pre-cast concrete members.

In at least some embodiments, the invention also comprises modular precast concrete formworks (MPCF) that includes joists, infill thin shells, beams, columns, and walls designed to eliminate or minimize the use of formwork and propping systems in concrete structures. The MPCF has been designed to withstand its self-weight together with construction related loads prior to on-site concreting. After installation, additional reinforcing bars (if required) are placed over the MPCF. A concrete overlay with a nominal thickness of not more than 70 mm is then placed over the MPCF to generate the final one-way or two-way flooring system. The MPCF looks a permanent formwork that is integrated and will be part of the final flooring system to bring the following superior benefits to the construction industry:

-   -   High-Quality Soffit Finishes;     -   Less on-site concreting (in this invention 1 m3 covers between         11.5 m2 to 14 m2 of floor area where as in the traditional         method it only covers between 3 m2 to 6 m2);     -   Less on-site reinforcing (Normally, single reinforcing mesh is         enough even for long spans);     -   No additional formworks;     -   Minor propping (single prop at mid span of joists in large span         floors or no prop for medium to small span floors);     -   Edge beams are equipped with proper connections for installation         of temporary suspended scaffolding platform. Hence, no need for         full scaffolding system;     -   The use of this invention offers a better serviceability limits         in the final floor system;     -   The invention deems to satisfy minimum 2 hour fire rating.     -   A rapid increase in the construction speed and a reduction in         construction costs.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows:

FIG. 1 is a perspective view of a one-way floor system 400 and a two-way floor system 400′ used in a building 1000 in accordance with a first and second embodiment of the present invention.

FIG. 2A is a perspective view of a pre-cast concrete member in the form of a plank member 100 in accordance with an embodiment of the present invention.

FIG. 2B is a right hand sectional view of the plank member 100.

FIG. 2C is a sectional view of a second embodiment of the plank member 100′.

FIG. 2D is a sectional view of a third embodiment of the plank member 100″.

FIG. 2E is a perspective view of a step plank unit 100′″.

FIG. 3 is an in-use sectional view of the plank member 100 having an indefinite length.

FIG. 4 is a sectional view of plank supporting member 110′ in accordance with an embodiment of the invention.

FIG. 5A is an in-use sectional view of the plank member 100″ supported upon the supporting member 110′.

FIG. 5B is a perspective view of the plank member 100″ supported upon the supporting members 110′ located at either lateral end of the plank member 100″.

FIG. 6A is a perspective view of a pre-cast joist 140 in accordance with an embodiment of the invention.

FIG. 6B is a sectional view of the pre-cast joist 140.

FIG. 6C is a sectional view of an alternative embodiment of a pre-cast joist 140′.

FIG. 7 is a sectional view of the two-way floor system 400″ in accordance with an embodiment of the present invention.

FIG. 8A is a U-shaped permanent formwork member 120′ in accordance with an embodiment of the present invention.

FIG. 8B is a sectional view of the U-shaped permanent formwork member 120′.

FIG. 9A is an L-shaped permanent formwork member 120 in accordance with an embodiment of the present invention.

FIG. 9B is a sectional view of the L-shaped permanent formwork member 120.

FIG. 10A is a perspective view of a pre-cast band beam 150 in accordance with an embodiment of the present invention.

FIG. 10B is a sectional view of the pre-cast band beam 150.

FIG. 11A is a perspective view of a pre-cast edge beam 160 in accordance with an embodiment of the present invention.

FIG. 11B is a sectional view of the pre-cast edge beam 160.

FIG. 12 is a perspective view of the band beam 150 supported on column units 170.

FIG. 13A is a sectional view of a square-shaped column unit 170 in accordance with an embodiment comprising column formwork members 300 being inter-connected to form a hollow portion to receive fresh concrete.

FIG. 13B is a sectional view of a rectangular column unit 170′.

FIG. 13C is a sectional view of the column formwork member 300.

FIG. 14 is a perspective view of the two-way flooring system 400′.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1 a building structure 1000 comprising a one-way floor system 400 and a two-way floor system 400′ in accordance with a first and second embodiment of the present invention. It shall be understood by the person skilled in the art that it is not necessary to use both flooring systems 400 and 400′ in the same building structure. By way of example, either a one-way floor system 400 or a two-way floor system 400′ may be used in an alternative building structure without departing from the spirit and scope of the invention.

Referring to FIGS. 1 and 7, the suspended one-way floor system is built by using modular precast concrete formworks. The system may comprise an array of parallel pre-cast concrete joists 140 positioned in a generally parallel arrangement. Each of the joists 140 spans between supporting elements such as a pair of elongate band beams 150. Each of the joists 140 is supported upon two band beams 150 positioned along either end of the joists 140. The band beams 150 and the joists 140 are generally arranged in a mutually perpendicular orientation. The band beams 150 are positioned and supported by upright columns or posts 170.

A plurality of pre-cast concrete members in the form of pan units 110 extend in between adjacently located pre-cast joists 140. Referring to FIGS. 5A and 5B, it is clearly illustrated that each pan unit 110 comprises a pre-cast plank 100″ that extends in between two lateral sides 101A and 101B. At each of the lateral sides, supporting structures 110′ are provided for supporting the pan unit 110 upon the two adjacently located joists 140.

Referring FIGS. 2A to 2E and FIG. 3, each of the plank units 100 or 100′ comprises a horizontal base portion 101. The longitudinal edges of the plank unit 100 or 100′ contain a recess 102 positioned at either lateral ends 101A and 101B of the plank units 100, 100′, or 100′″. The recess 102 allows the plank unit 100, 100′, 100′″ to be seated upon the supporting structures 110′. The plank units contain a horizontal mesh 103 that extend through the length of the plank units. Z shape wire ties 104 is connected to the main horizontal mesh 103 to enhance the cracking capacity of the recess portion of the plank units. Furthermore, mechanical shear connector 105 may be provided at the top surface of the plank unit to ensure 100% bonding between the plank units and the fresh concrete 108 above that. The soffit of the plank units 100, 100′, 100′″ is equipped with equally spaced cast-in-ferrules 106 to ease installation of a ceiling structure 109 that supports ceiling plaster boards 109′. Since the plank unit 100″ is used to make the pan unit 110, the top face of the pan unit 110 is also equipped with equally spaced cast-in-ferrules 107 for installation of the negative bending connectors 145 (refer to FIG. 7). The thickness of the plank units 100, 100′, and 100″ may vary between 50 mm to 80 mm. The thickness of the step plank unit 100′″ depends on the step height and is only used when a step needs to be generated within the floor system. The step plank unit 100′″ contains an upwardly portion 106 that extend along the plank unit. This portion act as an edge formwork to keep the wet concrete in the required level.

Alternatively, the installation of the one-way floor system 400 or two-way floor system 400′ may involve positioning a plurality of the plank units 100 or the pan units 110 in between adjacently located joists 140 or 140′. As Shown in FIGS. 4 and 5, the pan unit 110 comprises of the plank unit 100″ and the plank supporting unit 110′. During the installation, opposite ends of each of the pre-cast concrete pan unit 110 are supported upon oppositely arranged shelf portions of two adjacent joists 140 or 140′ (as illustrated in FIGS. 1 and 7).

The pre-cast plank supporting structure 110′ is elongate and extends along the length of the plank unit 100″. An outwardly facing surface of the pan unit 110 and the vertical surface of a supporting joist 140 or 140′ together define a receiving portion for receiving wet concrete during construction (best illustrated in FIG. 7). Referring to FIG. 4, each supporting unit 110′ comprises a seat portion 111 at its top surface to bond it to the recess 102 of the plank unit 100″. Each supporting structure 110′ comprises a bottom reinforcing bar 112 and the top reinforcing bars 113. The bottom reinforcing bars are connected to the top reinforcing bars using specific shear ligatures 114. The top face of the supporting structure 110′ is also equipped with equally spaced cast-in-ferrules 115 for installation of the negative bending connectors 145 (refer to FIG. 7). The pan unit 110 can be cast for providing span lengths of between 1750 mm and 2800 mm. The pre-cast concrete plank unit 110 or 110′ or 110″ are designed to withstand live loads of up to 4 kPa with total serviceability limit of span/250. The deflection under live load maybe kept under span/500.

Referring FIGS. 6A to 6B illustrate a joist 140 and FIG. 7 illustrates an alternative embodiment of the joist 140′. Each of these joists (140 or 140′ comprises a horizontal base portion 141; and a vertically oriented portion 142 extending substantially along the length of the joist 140 or 140′. The vertically oriented portion 142 comprises spaced apart upwardly extending surfaces. The spacing between the vertical surfaces is denoted by b1. The length of the top surface (b1) is less than the length of an in use bottom surface (b) of the base. The length of the top surface (b1) is in the range of 150 mm to 300 mm and length of the bottom surface (b) is in the range of 300 mm to 500 mm. Each of the vertical surfaces includes a chamfered portion located in between the shelf portion 141 and the respective almost vertical surfaces.

Shelf portions 141 are located adjacent on lateral sides of the vertically oriented portion 142 and each of the shelf portions 141 defines a seat for receiving a connecting portion of a pre-cast concrete pan unit 110 or plank unit 100′. The joist unit also includes the bottom reinforcing bars 143 located in the shelf portion 141 and the top reinforcing bars 144 that are partially located in vertically oriented portion 142. At least one of the top reinforcing bars, in some embodiments may be located outside of the vertically oriented portion 142 to enhance the connectivity between the joist and the fresh concrete 108 above that. The joist unit 140 may also be equipped with vertical ligature 146 that connect the bottom reinforcing bars 143 to the top reinforcing bars 144. The top surface of the joist 140 may also be equipped with equally spaced cast-in-ferrules 147 that are used to assemble the negative bending connectors 145 (refer to FIG. 7). To use the Joist 140 in the two-way action flooring system 400′, equally spaced voids 148 passing across the vertically oriented portions 142 to enhance the connectivity between joists 140 and the fresh concrete 108 and to assist with placing reinforcing bars or post-tensioning tendons/ducts for two-way floor system where the applied loads are transferred in direction of the joist 140 as well as in direction perpendicular to that.

The joists 140 or 140′ may be designed for covering spans of up to 12 m and the distance between adjacently located joists 140 and 140′ may vary between 1750 mm to 3300 mm. The joist unit 140′ (shown in FIG. 6C) is particularly useful when a step down in the floor system needs to be generated. The joist may be prestressed to shape downward curvature for covering longer spans or when high magnitude of construction loads are applied. The height of the vertically oriented portion may vary between 50 mm to 400 mm and the thickness of the base portion may vary between 50 mm and 120 mm.

In the presently described embodiment, the joist 140 has been designed to carry up to 6 kPa live load which is much higher than the required levels for both residential (less than 2 kPa) and commercial (mostly 3 kPa and in some location 4 kPa) buildings with a total deflection of less than span to 250 and deflection under live load of less than span to 500. Higher serviceability requirements can also be achieved by decreasing the clear distance between joists 140 when required. In the case when higher shear capacity is required, the web (142) of joists 140 and 140′ may be thickened at the support areas where the joist 140 or 140′ resting on the supporting elements (such as a band beam 150, edge beam 160, or a wall system 190—shown in FIG. 14).

The installation of the one-way floor system 400 may involve positioning a plurality of the pan units 110 or the plank unit 100′ or 100″ in between adjacently located joists 140 and 140′. Each of the pre-cast pan 110 or pre-cast plank unit 100′ and 100″ are adapted for receiving wet concrete, during construction, once these members (110, 100′, or 100″) are positioned in between the respective joists 140 or 140′.

Referring to FIGS. 8 and 9, permanent formwork flooring end plate units 120 and 120′ may also positioned, before pouring the wet concrete, at each of the respective edge portions of the pre-cast pan unit 110 or the plank units 100, 100′, and 100″. The flooring end plate units 120 or 120′ may be provided in the form of L-shaped 120 members (FIG. 9) or U-shaped 120′ members (FIG. 8).

The L-shaped end plate members 120 (depicted in FIG. 9) are used at the connecting location between each of the joists 140 and the joist supporting members (band beam unit 150 or edge beam unit 160, or wall unit 190). This arrangement has been more clearly illustrated in FIG. 14. The U-shaped end plate members 120′ (depicted in FIG. 8) are used in the second embodiment of the invention (400′, refer FIG. 15) when a two-way floor system is provided. The U-shaped flooring end plate 120′ can be positioned between the pre-cast pan units 110 and in line with rectangular or circular penetrations 148 in the joist 140 to allow two-way actions, one in direction of joist 140 and the other one in transverse direction relative to the joists 140. The flooring end plates 120 and 120′ comprise a reinforcing mesh 121 that is bent to conform to the shape of the flooring end plates, i.e. U Shape or L Shape. To enhance the connectivity of the flooring end plates to the fresh concrete, these permanent formwork members have been equipped with mechanical shear connectors 122.

Referring to FIGS. 10 to 12 illustrates the sectional and perspective views of the band beam unit 150 and edge beam unit 160. As discussed in the previous sections, the plurality of the pre-cast concrete joists 140 and 140′ are supported by a plurality of band beams 150 and or edge beams 160 that extends generally in a perpendicular direction relative to the general direction of the said pre-cast concrete joists 140 and 140′. When dealing with a low magnitude of the applied loads or dealing with short spans, the beam 150 may have a shape similar to the joist 140 but may be larger in size. Otherwise, the beam 150 comprises of two spaced apart formations 150A and 150B extending upwardly from the beam 150. The edge beam 160, contains one formation of 160A extending upwardly from the beam 160. The formations 150A and 150B extend along a length of the beam 150. Similarly, formation 160A also extends along a length of the edge beam. Joist receiving portions for the band beam 150 extend outwardly from the said formations 150A and 150B for supporting an end portion of a plurality of joists 140. Similarly joist receiving portions for the edge beam 160 extends outwardly from the formation 160A. The breadth for each of the formations (B) may vary between 100 to 300 mm depending on span of the band beam and magnitude of the applied loads. Thicker values may be used at the support areas of the beam to assist with transferring shear forces to the column 170. The height of the formations (H) may vary between 200 mm to 600 mm depending on span of the band beam and magnitude of the applied load. The thickness of the beam (T) may vary between 80 mm to 150.

Referring to FIGS. 10B and 11B, each of the band beams 150 further comprises top reinforcing bars 151 extending through an upper portion of the formation along a longitudinal direction of the band beam 150 and or the edge beam 160. Positive reinforcing bars also 155 extend along the beam 150 and 160. The beams 150 and 160 also comprise torsional and shear ligature bars 152 and 153 for providing additional shear strength characteristics to the beams 150 and 160. The shear ligature bars also assist with transferring shear forces acting at the interface of the beam 150 or the edge beam 160 and the overlay concrete poured on site. Circular or rectangular penetration openings 156 may also be provided through the 150A and 150B vertical portion of the beam 150. These openings reduce the total weight of the beam and generated interlock with the fresh concrete to enhance the composite actions between them. The beam 150 has also contains another penetration opening 157 within its horizontal portion along an underside to facilitate connection of the band beam 150 onto a supporting column, i.e. column 170. The beam element 150 also contains a recess 158 around the penetration 157. This will restrain the column head and transfer loads to the column via bearing at this area. A typical in-use perspective of assembly between column 170 and the band beam 150 has been shown in FIG. 13. Advantageously, each band beam 150 is provided as a single unit with a width of 800 to 2000 mm and no additional onsite works are required.

Referring FIG. 13, the cross section of column units 170 (square shape) and 170′ (rectangular shape) that are build using precast column formwork units 300. The column formwork units 300 comprises of a horizontal portion with a thickness of 50 mm to 70 mm and also contain a recess 301 at one of its edge. A portion of the column builder is extend downwardly by about 50 mm (302). The element also comprises internal reinforcing mesh 303. To enhance the cracking capacity of the edge of this unit, both external edges of the column formwork units 300 have been reinforced with edge wire ties 304. The column formwork units also contain connector elements 305 that are located at each end of the unit 300. Different widths of the column formwork units 300 can be connected to each other to shape a square shape (170) or a rectangular shape (170′) columns using structural adhesive. Mechanical connectors may also be used if required. Additional column cage containing longitudinal bars 306 and shear ligatures 307 may also be placed within the column cavity defined by the column formwork units 300 and secured in position using connector 305. A perspective view of column unit 170 have been shown in FIG. 13. The cavity of the column will then be filled with fresh concrete 308 on site.

Referring to FIG. 14, using modular precast concrete formwork to build a two-way slab system (400′) has been illustrated. The beams 150 is installed over the column unit 170. The edge beam 160 is spans between wall unit 190 and the beam unit 150. During the installation, beams 150 are connected to the column 170 using recess in the soffit of the beam. The joist units 140 are then placed between the beam unit 150 and the wall unit 190.

For two-way actions, U shape flooring end plates 120′ may be placed in front of rectangular or circular penetrations 148 (in Joists 140) and perpendicular to the Joists 140 to generate a monolithic transverse joist. The pan units 110 are then positioned between the joists 140 and the U shape permanent formworks 120′. The positive reinforcing or post-tensioning tendons/ducts can now be placed inside U shape flooring end plates and in transverse direction of the Joist 140. These are passed through the rectangular or circular penetrations 148 across all joints 140 and continued to the supporting beams 160. The floor system 400′ acts as one-way slab during construction phase and prior to removing props (that may be placed temporarily under the joists 140 or beams 150 and 160). After placement and curing of the overlay concrete, the final floor system 400′ acts as a two-way slab.

In at least some embodiments, it is expected that adopting the system 400 or 400′ is likely to provide the following advantages:

-   -   Increase the speed of construction;     -   Achieve high-quality surface finishes;     -   Enhance safety of labours working on a building;     -   Decrease construction cost;     -   Decrease the volume of the on-site concreting;     -   Decrease the amount of reinforcing bars that need to be placed         and arranged on-site;     -   Enhance the quality of the concrete structure;     -   Reduce the risk on third parties due to construction activities         as the building will be constructed in a short period of time         (compared with the current construction time).

In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. The term “comprises” and its variations, such as “comprising” and “comprised of” is used throughout in an inclusive sense and not to the exclusion of any additional features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.

Throughout the specification and claims (if present), unless the context requires otherwise, the term “substantially” or “about” will be understood to not be limited to the value for the range qualified by the terms.

Any embodiment of the invention is meant to be illustrative only and is not meant to be limiting to the invention. Therefore, it should be appreciated that various other changes and modifications can be made to any embodiment described without departing from the spirit and scope of the invention. 

The claims defining the invention are as follows:
 1. Formwork for constructing a floor system in a building, the formwork comprising: a plurality of pre-cast concrete joists positioned in a generally parallel arrangement, wherein one or more of the joists comprises: a horizontal base portion; and an upwardly directed portion extending substantially along the length of the joist, the upwardly directed portion having spaced apart surfaces extending upwardly from the base wherein respective shelf portions of the base are located adjacent said upwardly directed portion; a plurality of pre-cast concrete members for extending along a length of the joists for receiving wet concrete; and a supporting arrangement to support opposite ends each of the pre-cast concrete members upon oppositely arranged shelf portions of two adjacent joists.
 2. Formwork in accordance with claim 1 one or more of the pre-cast concrete members comprises a shell for receiving wet concrete, the shell being adapted to be coupled with respective downwardly directed supporting portions for supporting the shell on the oppositely arranged shelf portions of two adjacent joists.
 3. Formwork in accordance with claim 1 or 2 wherein the supporting portions are integrally formed with the pre-cast members.
 4. Formwork in accordance with any one of the preceding claims wherein an outer surface of the pre-cast concrete members in combination with the surface of the upwardly directed portion of the supporting joists positioned at opposite ends defines an in-use receiving portion for receiving wet concrete.
 5. Formwork in accordance with any one of the preceding claims wherein the pre-cast concrete members comprises edge portions extending along a length of the pre-cast concrete members wherein preferably at least a first edge portion extends along a first lateral side of the pre-cast concrete member and at least a second edge portion extends a second lateral side of the pre-cast concrete member.
 6. Formwork in accordance with claim 1 wherein one or more of the pre-cast concrete members comprises: a pan for receiving the wet concrete; and shoulder portions located at opposite ends of the pan, said shoulder portions being adapted to be supported on the oppositely arranged shelf portions of two adjacent joists.
 7. Formwork in accordance with claim 6 wherein the pan in combination with the surface of the upwardly directed portion of the supporting joists positioned at opposite ends defines an in-use receiving portion for receiving wet concrete.
 8. Formwork in accordance with any one of the preceding claims further comprising pre-cast concrete joists supported by a plurality of beams extending generally in a perpendicular direction relative to the general direction of the said pre-cast concrete joists.
 9. Formwork in accordance with claim 8 wherein the beam comprises a beam portion with a substantially flat profile with two spaced apart formations extending upwardly from the beam portion, the said formations extending along a length of the beam and joist receiving portions extending outwardly from the said formations for supporting an end portion of a plurality of joists.
 10. Formwork in accordance with any one of claim 8 or 9 wherein an outwardly projecting end portion of the plurality of joists is supported upon a joist receiving portion of the beam portion, the joist receiving portion of the beam preferably extending in a perpendicular direction relative to the said projecting end portions of the joist.
 11. Formwork in accordance with any one of claims 8 to 10 wherein an underside bottom surface of the beam substantially lies in the same plane as a bottom surface of the joist.
 12. Formwork in accordance with any one of the preceding claims further comprising: a first connecting mechanism for connecting a first joist positioned on a first lateral side of the beam with a second joist positioned on a second lateral side of the beam, said connecting mechanism being further adapted for preferably applying a negative bending force to the first and second joists during use; and a second connecting mechanism for connecting two adjacently located beams supported simultaneously on a column, the connector being provided for applying negative bending to said adjacently located beams.
 13. Formwork in accordance with any one of claims 8 to 12 further comprising column formwork members for forming columns to support said beams wherein each of the column formwork members can be inter-connected to define a hollow portion for receiving wet concrete.
 14. Formwork in accordance with claim 13 wherein end portions of each of the column formwork members comprises connecting portions for inter-connecting the column formwork members such that imaginary plane of a first column formwork member is transversely arranged relative to an imaginary plane of second column formwork member inter-connected with the first column formwork member.
 15. Formwork in accordance with any one of claim 13 or 14 wherein said locking portions extend along a longitudinal edge of the column formwork member such that in an inter-connected configuration the locking member is adapted to be received in a recess of another of said column formwork, said recess extending along a longitudinal edge of said another column formwork.
 16. Formwork in accordance with any one of the preceding claims further comprising one or more permanent formwork members for being positioned in between two spaced joists and wherein preferably the permanent formwork members comprise a substantially L-shaped or U-shaped cross section.
 17. Formwork in accordance with any one of the preceding claims wherein the joists of the formwork further comprise one or more apertures for receiving reinforcing bars, the reinforcing bars extending in a transverse direction relative to the general direction of the joists, the reinforcing bars being adapted for being tensioned (by way of post-tensioning) after pouring concrete into the pre-cast concrete receiving members.
 18. Formwork in accordance with any one of the preceding claims wherein at least one the pre-cast concrete members comprises a stepped configuration having an in-use upper portion and an in-use lower portion.
 19. A pre-cast concrete joist comprising: a horizontal base portion; and an upwardly directed portion extending substantially along the length of the joist, the upwardly directed portion having spaced apart surfaces extending upwardly from the base wherein shelf portions of the base are located adjacent said upwardly directed portion, each of the shelf portions defining a seat for receiving a connecting portion of a pre-cast concrete pan member or a pre-cast concrete shell member wherein height of the upwardly directed portion is equal to or greater than vertical height of the said shelf portions.
 20. A pre-cast concrete member for being positioned in between and supported spaced apart joists or beams, the precast member extending along a length of the joists or beams for receiving wet concrete, the precast member comprising a supporting arrangement to support opposite ends each of the pre-cast concrete members upon oppositely arranged joists or beams.
 21. A method of constructing a suspended floor in a building, the method comprising the steps of: positioning a plurality of pre-cast concrete joists in a generally parallel arrangement, wherein one or more of the joists comprises: a horizontal base portion; and an upwardly directed portion extending substantially along the length of the joist, the upwardly directed portion having spaced apart surfaces extending upwardly from the base wherein shelf portions of the base are located adjacent said vertical portion; positioning a plurality of pre-cast concrete members in between adjacently located joists, said pre-cast concrete members being positioned for extending along a length of the joists for receiving poured concrete; supporting opposite ends of each of the pre-cast concrete members upon oppositely arranged shelf portions of two adjacent joists; and pouring fresh concrete into a receiving portion defined by the pre-cast concrete members. 